Damage to automotive vehicle coatings due to the impact of road debris on vehicles is a recognized problem. Certain portions of vehicles are more susceptible to such damage because they are in a direct line of flight for gravel, stones and other debris. For example, the lower side panels of cars are frequently damaged in this way.
To address this problem, it is known to use a two layer chip resistant coating system on vehicle parts over electrodeposited primer coatings. For example, U.S. Pat. No. 4,971,837 to Martz et al. discloses a wet on wet application and cure process for making a chip resistant coating. This process involves applying a second coating composition onto a first coating composition while the first is still uncured and then curing both layers at an elevated temperature.
Such wet on wet two coat systems, if used on the entire surface area of the vehicle, can increase costs and application complexity. Therefore, such wet on wet systems may be used only on limited vehicle areas most susceptible to damage from road debris. Typically, at the interface between a two coat portion of a vehicle and a one coat portion of a vehicle there is a transition zone in which the additional coat in a two coat system is feathered out. In the case in which the additional coat is a free-radically intiated curable coating composition, such feathering out can lead to curing problems. For example, at thin film thicknesses in the feathering out zone, cure can be inhibited by oxygen. Such coating compositions are also susceptible to cure inhibition by cationically electrodeposited primer compositions which are typically applied prior to application of anti-chip coatings.
The present invention addresses the foregoing problems present in the industry and provides a chip-resistant coating having good thin film cure and useful in wet on wet applications.